I think this is a dangerous fallacy many of us run into: judging content by it's domain name. Would the same content on a completely different domain change the prejudice towards the contents of the text? Similarly would a url shortener hide the potential bias? By seeing the domain name in this case one could assume a bias towards single sex schools. At least the author of that presence would be frank about it. Similarly couldn't it be that the author chose singlesexschool.org for it's catchiness and still favor coed?

While this particular article presents facts in favor of single sex schools, I would think that our duty is to educate our kids and peers to critically question anything they read and at least do a little research (scanning the site to get a basic understanding of the agenda the author may be pushing; to follow the supposedly supporting links, ...).